I would classify the following:Telemetry:anything that is sent down that originates from the satelliteTransponder: anything that relays information from groundTelecommand: anything used for controlling the satellite.

This last option would not be used a lot, but it should be mentioned.

APRS would be transponder, SSTV would be telemetry, unless its a SSTV relay, in which case it would be transponder.